Interpretive Summary: Equine feed contamination and toxicology.
By: Jackie Walling
A recent article published in the 2018 March issue of Translational Animal Science explored feed contamination and toxicology in equines focusing on the effects of chemical contaminants. Common causes of contamination result from misformulation, adulteration, and natural contaminants which can be determined by extracting samples of affected feeds for analysis.
Indications of contaminated feed can be as simple as refusal of food all the way to having horses on the same diet at the same facilities and surrounding barns show up with identical clinical signs of feed poisoning. Suspected contamination should be immediately reported to the manufacturer, state vet and FDA so a recall can be issued and an investigation opened to document the case. Samples of the feed will be collected and deposited in tamper evident containers, sent to a lab, and tracked using chain-of-custody tags.
Typically, contaminants are not evenly distributed throughout the feed. Hot spots, mold, discoloration, and moisture indicate contamination in mixed feeds, pellets, and hay. Urine, feces, whole blood, and serum sample should be collected from live affected animals. If the animal has died, either the carcass should be submitted for evaluation or a full set of tissues should be collected.
Misformulation is one of the most common causes of contamination and occurs when feed produced deviates from the original recipe resulting in either an overabundance or lack of a nutrient. This can have drastic consequences depending on the nutrient. For horses, too much Vitamin D can cause hypercalcemia (too much calcium in the blood) targeting the kidneys with metastatic mineralization (deposition of minerals in tissue).
Adulteration in horse feed is typically caused by ionophores or antibiotics not part of the original recipe. Ionophores cause an imbalance of ions in cell plasma because they augment movement of ions, normally impermeable to cells, across lipid membranes. Known as Ionophore toxicosis, this imbalance causes changes in cellular pH, polarization, neurotransmitter release, and ATP production. Antibiotics attack the composition of natural gut flora allowing Clostridium difficile to colonize and cause severe complications.
Natural contaminants include insects and mycotoxins. Blister beetles contain a molecule, cantharidin, responsible for attacking structures holding epithelial cells together resulting in blisters. These bugs are commonly found in hay and blister the mucosa of the digestive tract as it passes through the horse. The mycotoxin, fumonisin, is prevalent in the United States. Known as “moldy corn poisoning,” it is associated with the pathognomonic lesion, leukoencephalomalacia, which means “softening of the white matter of the brain”. Because of the damage caused to the nervous system, affected horses have a grim prognosis.
Lastly, though a biologically caused contaminant, Botulism is caused by accidental incorporation of small animal carcasses in feed, or carrion. Botulinum neurotoxins prevent acetylcholine release from synapses causing paralysis. Early signs of botulism include inability of the horse to get up and swallow. Recovery is slim, but a vaccine can be utilized to help prevent one type of Botulism.
For an in depth look at the contaminants in horse feeds, read “Equine feed contamination and toxicology” in Translational Animal Science.